1. Field of Invention
The present invention relates generally to a method and apparatus for cleaning a semiconductor processing system. More specifically, the invention relates to a method of cleaning a semiconductor process system comprising a turbomolecular pump coupled to a process chamber, using a fluorinated gas.
2. Description of the Background Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually demands faster circuitry, greater circuit density, and increased functionality. As the circuit density decreases, it has become increasingly important to create the circuit structures precisely and repeatably in order to effectively utilize thinner films. In order to obtain precision and repeatability in circuit structures from wafer to wafer, processing windows for parameters used when forming thin films such as chamber pressure, must correspondingly be tighten and better controlled.
A material commonly used in the circuit structures utilizing thin films is phosphorous doped, silicon dioxide, commonly known as phosphorous doped glass (PSG). Phosphorous doped glass is generally used as a passivation film or as a pre-metal dielectric. Phosphorous doped glass is commonly formed by chemical vapor deposition (CVD) processes that react a silicon source (e.g., silane or tetraethylorthosilicate (TEOS)) with an oxidizing agent (e.g., O2 and HO2) at elevated temperatures. Phosphorous doped glass may also be formed using plasma enhanced chemical vapor deposition (PECVD) and high density plasma chemical vapor deposition (HDP-CVD) processes that allow for deposition of phosphorous doped glass at lower temperatures.
During both PECVD and HDP-CVD processes, chamber pressure has been found to drift higher over the course of deposition of phosphorous doped glass upon a wafer. This process drift is aggravated over the course of multiple depositions when processing a batch of wafers. The process drift causes variation in deposition rates across the batch, and variation in the phosphorous doping levels found in films wafer to wafer. As a result, the conformity required to produce consistent circuit structures over the course of a process run is compromised. Such non-uniformity is a limiting factor in the use of circuit structures comprising thin films.
The cause of the pressure drift is attributed in part to the contamination of a turbomolecular pump used to maintain chamber pressure during processing. During the deposition of silicon dioxide, a phosphorous containing compound adheres to the turbomolecular pump components thus reducing the pump""s efficiency and ability to maintain a predetermined chamber pressure.
Typical semiconductor process systems having cleaning capability generally do not clean the turbomolecular pump. Conventional system designs rely upon the high rotational velocity and a sufficiently low pressure conditions within the turbomolecular pump to prevent deposition upon the pump components. As such, chamber cleaning processes are generally vented through a roughing pump and by-pass the turbomolecular pump. As a result, deposits within the turbomolecular pump are never removed during conventional cleaning processes. These deposits increase over time, causing the pressure characteristics of the turbomolecular pump to degrade until the turbomolecular pump becomes unsuitable for use when depositing thin films and requires replacement.
Therefore, there is a need in the art for a semiconductor process system that removes contamination from a turbomolecular pump.
One aspect of the invention provides a semiconductor wafer processing system comprising a chamber, a cleaning system, a pumping system coupled and a control system. The cleaning and pumping systems are coupled to the chamber. The control system is coupled to the cleaning and pumping systems. The chamber pumping system comprises a rough pump and a turbomolecular pump. The control system causes a gate valve disposed between the turbomolecular pump and the chamber to open and divert a portion of a cleaning agent to be drawn from the chamber by the rough pump through the turbomolecular pump. As the cleaning agent passes through the turbomolecular pump, the turbomolecular pump is cleaned of surface contaminants, thus enabling the turbomolecular pump to maintain substantially constant and repeatable pressures within the chamber over multiple wafer processing.